SEGMENT AND RELATED INFORMATION - Financial Data for Business Segments (Details)				1 Months Ended		3 Months Ended			12 Months Ended
	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jan. 17, 2020 USD ($)	Jan. 31, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) utility
Segment Reporting Information [Line Items]
Total operating revenues									$ 20,375,000,000	$ 21,419,000,000	$ 23,495,000,000
Depreciation and amortization									3,518,000,000	3,038,000,000	3,131,000,000
Interest income									37,000,000	60,000,000	38,000,000
Operating income (loss)									4,885,000,000	7,736,000,000	4,191,000,000
Earnings from equity method investments									153,000,000	162,000,000	148,000,000
Interest expense									1,821,000,000	1,736,000,000	1,842,000,000
Income taxes (benefit)									393,000,000	1,798,000,000	449,000,000
Segment net income (loss)									3,119,000,000	4,739,000,000	2,226,000,000
Goodwill	$ 5,280,000,000					$ 5,280,000,000		$ 5,280,000,000	5,280,000,000	5,280,000,000	5,315,000,000
Total Assets	122,935,000,000					122,935,000,000		118,700,000,000	122,935,000,000	118,700,000,000	116,914,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000	0	1,060,000,000
Gain (loss) on dispositions									66,000,000	2,588,000,000	301,000,000
Lease, impairment loss						52,000,000	$ 154,000,000	17,000,000	206,000,000	0	0
Lease, impairment loss, after tax						31,000,000	$ 74,000,000	13,000,000
Impairment charges									0	168,000,000	210,000,000
Net gain on dispositions									65,000,000	2,569,000,000	291,000,000
Goodwill impairment						0
Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									16,497,000,000	17,095,000,000	18,571,000,000
Depreciation and amortization									2,941,000,000	2,472,000,000	2,565,000,000
Interest income									30,000,000	47,000,000	31,000,000
Earnings from equity method investments									0	5,000,000	(1,000,000)
Interest expense									976,000,000	987,000,000	1,035,000,000
Income taxes (benefit)									517,000,000	708,000,000	207,000,000
Segment net income (loss)									3,115,000,000	3,268,000,000	2,304,000,000
Goodwill	2,000,000					2,000,000		2,000,000	2,000,000	2,000,000	2,000,000
Total Assets	98,041,000,000					98,041,000,000		94,650,000,000	98,041,000,000	94,650,000,000	93,959,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
All Other
Segment and Related Information (Textual) [Abstract]
Lease, impairment loss									206,000,000
Lease, impairment loss, after tax									105,000,000
Operating Segments | Traditional Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									15,135,000,000	15,569,000,000	16,843,000,000
Depreciation and amortization									2,447,000,000	1,993,000,000	2,072,000,000
Interest income									26,000,000	38,000,000	23,000,000
Earnings from equity method investments									0	2,000,000	(1,000,000)
Interest expense									825,000,000	818,000,000	852,000,000
Income taxes (benefit)									514,000,000	764,000,000	371,000,000
Segment net income (loss)									2,877,000,000	2,929,000,000	2,117,000,000
Goodwill	0					0		0	0	0	0
Total Assets	85,486,000,000					85,486,000,000		81,063,000,000	85,486,000,000	81,063,000,000	79,382,000,000
Operating Segments | Southern Power | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									1,733,000,000	1,938,000,000	2,205,000,000
Depreciation and amortization									494,000,000	479,000,000	493,000,000
Interest income									4,000,000	9,000,000	8,000,000
Earnings from equity method investments									0	3,000,000	0
Interest expense									151,000,000	169,000,000	183,000,000
Income taxes (benefit)									3,000,000	(56,000,000)	(164,000,000)
Segment net income (loss)									238,000,000	339,000,000	187,000,000
Goodwill	2,000,000					2,000,000		2,000,000	2,000,000	2,000,000	2,000,000
Total Assets	13,235,000,000					13,235,000,000		14,300,000,000	13,235,000,000	14,300,000,000	14,883,000,000
Operating Segments | Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
Depreciation and amortization									500,000,000	487,000,000	500,000,000
Interest income									5,000,000	3,000,000	4,000,000
Earnings from equity method investments									141,000,000	157,000,000	148,000,000
Interest expense									231,000,000	232,000,000	228,000,000
Income taxes (benefit)									173,000,000	130,000,000	464,000,000
Segment net income (loss)									590,000,000	585,000,000	372,000,000
Goodwill	5,015,000,000					5,015,000,000		5,015,000,000	5,015,000,000	5,015,000,000	5,015,000,000
Total Assets	22,630,000,000					22,630,000,000		21,687,000,000	22,630,000,000	21,687,000,000	21,448,000,000
Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues									596,000,000	690,000,000	1,213,000,000
Depreciation and amortization									77,000,000	79,000,000	66,000,000
Interest income									6,000,000	16,000,000	8,000,000
Earnings from equity method investments									12,000,000	0	2,000,000
Interest expense									614,000,000	517,000,000	580,000,000
Income taxes (benefit)									(297,000,000)	960,000,000	(222,000,000)
Segment net income (loss)									(592,000,000)	908,000,000	(453,000,000)
Goodwill	263,000,000					263,000,000		263,000,000	263,000,000	263,000,000	298,000,000
Total Assets	3,168,000,000					3,168,000,000		3,511,000,000	3,168,000,000	3,511,000,000	3,285,000,000
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues									(152,000,000)	(158,000,000)	(198,000,000)
Depreciation and amortization									0	0	0
Interest income									(4,000,000)	(6,000,000)	(5,000,000)
Earnings from equity method investments									0	0	(1,000,000)
Interest expense									0	0	(1,000,000)
Income taxes (benefit)									0	0	0
Segment net income (loss)									6,000,000	(22,000,000)	3,000,000
Goodwill	0					0		0	0	0	0
Total Assets	(904,000,000)					(904,000,000)		(1,148,000,000)	(904,000,000)	(1,148,000,000)	(1,778,000,000)
Intersegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Total operating revenues									(371,000,000)	(412,000,000)	(477,000,000)
Depreciation and amortization									0	0	0
Interest income									0	0	0
Earnings from equity method investments									0	0	0
Interest expense									0	0	0
Income taxes (benefit)									0	0	0
Segment net income (loss)									0	0	0
Goodwill	0					0		0	0	0	0
Total Assets	(680,000,000)					(680,000,000)		(713,000,000)	(680,000,000)	(713,000,000)	(306,000,000)
Georgia Power
Segment Reporting Information [Line Items]
Total operating revenues									8,309,000,000	8,408,000,000	8,420,000,000
Depreciation and amortization									1,425,000,000	981,000,000	923,000,000
Operating income (loss)									1,972,000,000	2,461,000,000	1,289,000,000
Interest expense									425,000,000	409,000,000	397,000,000
Income taxes (benefit)									152,000,000	472,000,000	214,000,000
Total Assets	47,080,000,000					47,080,000,000		44,541,000,000	47,080,000,000	44,541,000,000
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000	0	1,060,000,000
Georgia Power | Plant Vogtle Units 3 And 4
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4	176,000,000	$ 149,000,000
Estimated loss on Plant Vogtle Units 3 and 4, net of tax	131,000,000	$ 111,000,000
Georgia Power | Traditional Operating Companies | Plant Vogtle Units 3 And 4
Segment and Related Information (Textual) [Abstract]
Estimated loss on Plant Vogtle Units 3 and 4									325,000,000		1,100,000,000
Estimated loss on Plant Vogtle Units 3 and 4, net of tax									242,000,000		800,000,000
Southern Power
Segment Reporting Information [Line Items]
Total operating revenues									1,733,000,000	1,938,000,000	2,205,000,000
Depreciation and amortization									494,000,000	479,000,000	493,000,000
Operating income (loss)									342,000,000	395,000,000	242,000,000
Interest expense									151,000,000	169,000,000	183,000,000
Income taxes (benefit)									3,000,000	(56,000,000)	(164,000,000)
Segment net income (loss)									238,000,000	339,000,000	187,000,000
Total Assets	13,235,000,000					13,235,000,000		14,300,000,000	13,235,000,000	14,300,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									39,000,000	24,000,000	3,000,000
Impairment charges									0	3,000,000	156,000,000
Impairment charges, after tax											117,000,000
Net gain on dispositions									39,000,000	23,000,000	2,000,000
Southern Company Gas
Segment Reporting Information [Line Items]
Total operating revenues									3,434,000,000	3,792,000,000	3,909,000,000
Depreciation and amortization									500,000,000	487,000,000	500,000,000
Operating income (loss)									812,000,000	770,000,000	915,000,000
Earnings from equity method investments									141,000,000	157,000,000	148,000,000
Interest expense									231,000,000	232,000,000	228,000,000
Income taxes (benefit)									173,000,000	130,000,000	464,000,000
Segment net income (loss)									590,000,000	585,000,000	372,000,000
Goodwill	5,015,000,000					5,015,000,000		5,015,000,000	5,015,000,000	5,015,000,000
Total Assets	22,630,000,000					22,630,000,000		21,687,000,000	22,630,000,000	21,687,000,000	21,448,000,000
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									22,000,000	0	291,000,000
Impairment charges									0	115,000,000	42,000,000
Net gain on dispositions									22,000,000	0	291,000,000
Goodwill impairment						0
Southern Company Gas | Gas distribution operations
Segment Reporting Information [Line Items]
Goodwill	4,034,000,000					4,034,000,000		4,034,000,000	4,034,000,000	4,034,000,000
Southern Company Gas | Gas marketing services
Segment Reporting Information [Line Items]
Goodwill	981,000,000					981,000,000		981,000,000	981,000,000	981,000,000
Segment and Related Information (Textual) [Abstract]
Net gain on dispositions											(33,000,000)
Net gain on dispositions, after tax											(67,000,000)
Disposal group, including discontinued operation, revenue											55,000,000
Southern Company Gas | Operating Segments
Segment Reporting Information [Line Items]
Total operating revenues									3,466,000,000	3,810,000,000	3,930,000,000
Depreciation and amortization									470,000,000	454,000,000	453,000,000
Operating income (loss)									814,000,000	924,000,000	1,013,000,000
Earnings from equity method investments									141,000,000	162,000,000	145,000,000
Interest expense									228,000,000	225,000,000	227,000,000
Income taxes (benefit)									178,000,000	200,000,000	495,000,000
Segment net income (loss)									592,000,000	677,000,000	435,000,000
Total Assets	23,040,000,000					23,040,000,000		22,228,000,000	23,040,000,000	22,228,000,000	21,918,000,000
Southern Company Gas | Operating Segments | All Other
Segment Reporting Information [Line Items]
Total operating revenues									36,000,000	44,000,000	55,000,000
Depreciation and amortization									30,000,000	33,000,000	47,000,000
Operating income (loss)									(7,000,000)	(154,000,000)	(98,000,000)
Earnings from equity method investments									0	(5,000,000)	3,000,000
Interest expense									3,000,000	7,000,000	1,000,000
Income taxes (benefit)									(5,000,000)	(70,000,000)	(31,000,000)
Segment net income (loss)									(2,000,000)	(92,000,000)	(63,000,000)
Total Assets	11,336,000,000					11,336,000,000		10,759,000,000	11,336,000,000	10,759,000,000	11,112,000,000
Southern Company Gas | Operating Segments | Gas distribution operations
Segment Reporting Information [Line Items]
Total operating revenues									2,952,000,000	3,028,000,000	3,186,000,000
Depreciation and amortization									442,000,000	422,000,000	409,000,000
Operating income (loss)									655,000,000	573,000,000	904,000,000
Earnings from equity method investments									0	0	0
Interest expense									192,000,000	187,000,000	178,000,000
Income taxes (benefit)									114,000,000	63,000,000	409,000,000
Segment net income (loss)									390,000,000	337,000,000	334,000,000
Total Assets	19,090,000,000					19,090,000,000		18,204,000,000	19,090,000,000	18,204,000,000	17,266,000,000
Southern Company Gas | Operating Segments | Gas Pipeline Investments
Segment Reporting Information [Line Items]
Total operating revenues									32,000,000	32,000,000	32,000,000
Depreciation and amortization									5,000,000	5,000,000	5,000,000
Operating income (loss)									20,000,000	20,000,000	20,000,000
Earnings from equity method investments									141,000,000	162,000,000	145,000,000
Interest expense									29,000,000	30,000,000	34,000,000
Income taxes (benefit)									33,000,000	58,000,000	28,000,000
Segment net income (loss)									99,000,000	94,000,000	103,000,000
Total Assets	1,597,000,000					1,597,000,000		1,678,000,000	1,597,000,000	1,678,000,000	1,763,000,000
Southern Company Gas | Operating Segments | Wholesale gas services
Segment Reporting Information [Line Items]
Total operating revenues									74,000,000	294,000,000	144,000,000
Depreciation and amortization									1,000,000	1,000,000	2,000,000
Operating income (loss)									20,000,000	219,000,000	70,000,000
Earnings from equity method investments									0	0	0
Interest expense									4,000,000	5,000,000	9,000,000
Income taxes (benefit)									3,000,000	52,000,000	4,000,000
Segment net income (loss)									14,000,000	163,000,000	38,000,000
Total Assets	850,000,000					850,000,000		850,000,000	850,000,000	850,000,000	1,302,000,000
Southern Company Gas | Operating Segments | Gas marketing services
Segment Reporting Information [Line Items]
Total operating revenues									408,000,000	456,000,000	568,000,000
Depreciation and amortization									22,000,000	26,000,000	37,000,000
Operating income (loss)									119,000,000	112,000,000	19,000,000
Earnings from equity method investments									0	0	0
Interest expense									3,000,000	3,000,000	6,000,000
Income taxes (benefit)									28,000,000	27,000,000	54,000,000
Segment net income (loss)									89,000,000	83,000,000	(40,000,000)
Total Assets	1,503,000,000					1,503,000,000		1,496,000,000	1,503,000,000	1,496,000,000	1,587,000,000
Southern Company Gas | Intersegment Eliminations
Segment Reporting Information [Line Items]
Total operating revenues									(68,000,000)	(62,000,000)	(76,000,000)
Depreciation and amortization									0	0	0
Operating income (loss)									5,000,000	0	0
Earnings from equity method investments									0	0	0
Interest expense									0	0	0
Income taxes (benefit)									0	0	0
Segment net income (loss)									0	0	0
Total Assets	$ (11,746,000,000)					$ (11,746,000,000)		$ (11,300,000,000)	(11,746,000,000)	(11,300,000,000)	(11,582,000,000)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas | Gas distribution operations
Segment and Related Information (Textual) [Abstract]
Net gain on dispositions											324,000,000
Net gain on dispositions, after tax											$ 16,000,000
Number of distribution utilities | utility											3
Disposal group, including discontinued operation, revenue											$ 244,000,000
Mankato | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Power
Segment and Related Information (Textual) [Abstract]
Gain on sale									39,000,000
Gain on sale, after tax									23,000,000
Gain (loss) on dispositions			$ 39,000,000
Gain (loss) on dispositions, after tax			$ 23,000,000
Plant Nacogdoches | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Power
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										23,000,000
Gain (loss) on dispositions, after tax										88,000,000
Gulf Power | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions				$ 2,600,000,000						2,600,000,000
Gain (loss) on dispositions, after tax				$ 1,400,000,000						1,400,000,000
PowerSecure International, Inc. Lighting Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										(58,000,000)
Gain (loss) on dispositions, after tax										(52,000,000)
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions										(24,000,000)
Gain (loss) on dispositions, after tax					$ (67,000,000)					(17,000,000)
Net gain on dispositions											291,000,000
Net gain on dispositions, after tax											(51,000,000)
Goodwill impairment					$ 42,000,000						$ 42,000,000
Jefferson Island | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Gain (loss) on dispositions									22,000,000
Gain (loss) on dispositions, after tax									$ 16,000,000
Natural Gas Storage Facility | Southern Company Gas
Segment and Related Information (Textual) [Abstract]
Impairment charges										115,000,000
Impairment charges, after tax										$ 86,000,000